The difference between over mould with

There are some difference between over mold and double mould at mold structure and mold manufacture:
A, double mould :  inject two kinds of plastic material in one injection machine ,double injection , but the part just depanning one time , general , this injection technics also be thought to be double base injection , which usually made by one mold , and need special double injection machine to make part.
B, over mould (postforming ): two kinds of plastic material may not be injected in one injection machine , which should be postforming , but the part just depanning one time . it is to say that the part be taked out from one mold , then put it to another mold and be injected at second injection . so this injection technics need two sets of mold to finish the part , and do not need special double injection machine .

The Summarize for over mould and double mould
Post forming mold (include over mould ), should take note of the location of Hard rubber part , which should be reliable seal and also should have back draft hole on the part , which can prevent from frictional pullar and distortion .
The double mould is more and more popular in market , as this technics can make the appearance of part more pretty, can change the color easily and not need to coating , but which construction cost is too expensive , and high  technical requirements

1， The two shapes of cavity is different , which will be molded to part separately  . but the two shape of core is the same.

2.  The cover and cavity must be anastomotic  when be rotated 180 by center . and must check this when design the part.
3，Take note of the location of ejector pin , the minimum distance is 210 mm. the large mold must increase the quantity of ejector hole properly . moreover , as the ejector pin of injection machine is not enough long ,  so we must lengthen ejector pin when we design the mould , and the length of ejector should be more 150 mm than bottom plate of mold base.
At the same time , we should design two locating ring on the bottom plate of cavity .
4， The total thickness of cover panel and A plate should not less than 170 mm. please examine the other reference data of this style of injection machine carefully , such as , the max molar thickness , minimum molar thickness , distance of ejector hole, and so on .
5，The gate of three plates mold had better to  be designed to demould automatic , especially need pay attention to the demould action of soft gate , which should be confirmed whether is reliable .
6  The depth of ventro sprue need not more than 65 mm,  and the distance from the top of sprue of large gate to centre of mold base should not less than 150mm.
7  When we design the cavity of second injection ,  in order to avoid to rubbing the part gate which had already molded at first time , we can design the portion is empty . but must consider the strength of every sealing compound carefully , it is to say , should consider that if the plastic will be deformed when the injection pressure is large. Which may be cause the flash at second injection .
8  When injecting plastic ,  the part size can be a little large when make the first injection , which can make it will be more tight with the other cavity , so as to be sealing compound .
9， When do the second injection , should consider whether the flow of plastic will flush out the molding part at first time , and make the location be deformed . if it will be ,  must try our best to improve this .
10  Before combining the A Plate and B plate , should consider whether the slider or lifter of cover will be reset and crush cover can be reset .
11  The water running of two cavity and core should be adequate as possible , and also need be balanced and same .

12  The most of case is injecting the hard gum of part first , and then injecting the soft gum . because the soft gum will be deformed easily .
13  In order to make two kinds of plastic be tight , should consider the stickiness between the material , and also should consider the surface roughness of mold .
There are special TPU for double injection ,  the mold surface is more smooth ,  the more tight them will be .
14  Consider the location of cover and cavity, all the pitch distance of insert should be larger as possible , should be above 0.1 mm.